Adding multiple executables in CMake

Question

My code in a C++ project is organised as follows

• I have several .cpp and .h files which contains my classes
• I have several .cxx files which have to be compiled against the .cpp files and some external libraries.

Now, each of the .cxx files have a main() method, so I need to add a different executable for each of these files having the same name as the file.

Also, these .cxx files might not get linked to the same external libraries.

I want to write this build in CMake, in which I am kind of a newbie, how do I go about this?

Answer 1

My suggestion is to tackle this in two phases:

1. Build a library from the .cpp and .h files, using add_library
2. Iterate through all your .cxx files and create an executable from each, using add_executable and foreach

Build the library

This could be something as simple as

file( GLOB LIB_SOURCES lib/*.cpp )
file( GLOB LIB_HEADERS lib/*.h )
add_library( YourLib ${LIB_SOURCES} ${LIB_HEADERS} )

Build all the executables

Simply loop over all the .cpp files and create separate executables.

# If necessary, use the RELATIVE flag, otherwise each source file may be listed 
# with full pathname. RELATIVE may makes it easier to extract an executable name
# automatically.
# file( GLOB APP_SOURCES RELATIVE app/*.cxx )
file( GLOB APP_SOURCES app/*.cxx )
foreach( testsourcefile ${APP_SOURCES} )
    # Cut off the file extension and directory path
    get_filename_component( testname ${testsourcefile} NAME_WE )
    add_executable( ${testname} ${testsourcefile} )
    # Make sure YourLib is linked to each app
    target_link_libraries( ${testname} YourLib )
endforeach( testsourcefile ${APP_SOURCES} )

Some warnings:

• file( GLOB ) is usually not recommended, because CMake will not automatically rebuild if a new file is added. I used it here, because I do not know your sourcefiles.
• In some situations, source-files may be found with a full pathname. If necessary, use the RELATIVE flag for file(GLOB ...).
• Manually setting the source-files requires a change to CMakeLists.txt, which triggers a rebuild. See this question for the (dis-)advantages of globbing.

Concerning "general" CMake info, I advise you to read some of the broad "CMake Overview" questions already asked here on stackoverflow. E.g.:

• https://stackoverflow.com/questions/2186110/cmake-tutorial
• What are the dusty corners a newcomer to CMake will want to know?

Answer 2

I find myself in a similar situation when organizing an OpenGL project with multiple sample files where each of these files contain a main method.

The settings below will generate a separate executable per c/cpp file as well as copying required dependencies to the target bin folder.

Folder Structure

my-project
│── ch01_01.c
│── ch02_01.cpp
│── CMakeLists.txt
│── Resources
│   │── Libraries
│   │   │── glew
│   │   │   │── bin
│   │   │   │── include
│   │   │   │── lib
│   │   │── glfw    
│   │   │   │── include 
│   │   │   │── lib 

CMakeLists.txt

cmake_minimum_required (VERSION 3.9)

project ("my-project")

include_directories(Resources/Libraries/glew/include
                    Resources/Libraries/glfw/include)

link_directories(Resources/Libraries/glew/lib
                 Resources/Libraries/glfw/lib)

link_libraries(opengl32.lib
               glew32.lib
               glfw3.lib)

set(CMAKE_EXE_LINKER_FLAGS "/NODEFAULTLIB:MSVCRT")

file(GLOB SOURCE_FILES *.c *.cpp)

foreach(SOURCE_PATH ${SOURCE_FILES})

    get_filename_component(EXECUTABLE_NAME ${SOURCE_PATH} NAME_WE)

    add_executable(${EXECUTABLE_NAME} ${SOURCE_PATH})

    # Copy required DLLs to the target folder
    add_custom_command(TARGET ${EXECUTABLE_NAME} POST_BUILD
                       COMMAND ${CMAKE_COMMAND} -E copy_if_different "${CMAKE_SOURCE_DIR}/Resources/Libraries/glew/bin/glew32.dll" 
                                                                     "${CMAKE_BINARY_DIR}/glew32.dll")

endforeach(SOURCE_PATH ${SOURCE_FILES})

Optional Steps

In Visual Studio

• Open the project with 'Open a local Folder' option in the Start Window

• When adding a new file you may either:

  • Cancel the dialog asking to automatically add_executable to CMakeLists.txt
  • Disable this behavior by unchecking 'Enable automatic CMake script modification for file operations from folder view' in Tools > Options > CMake

As newly added files are not picked up automatically as CMakeLists.txt is never changed, simply regenerate the cache like so:

• Project > CMake Cache (x64-Debug) > Delete Cache
• Project > Generate Cache for my-project

Now you may simply right click a given c/cpp file and Set as Startup Item to be able to debug it with F5.

Environment

• cmake version 3.18.20081302-MSVC_2
• Microsoft Visual Studio Community 2019 Version 16.8.3

Starter Template

I put together this starter template on GitHub in case you are interested.

Answer 3

This CMakeLists.txt works for my OpenCV project
assuming *.cpp files are in the same directory as CMakeLists.txt

cmake_minimum_required(VERSION 3.5)

project(opencv LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(OpenCV REQUIRED)
include_directories( ${OpenCV_INCLUDE_DIRS} )

file( GLOB APP_SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp )
foreach( sourcefile ${APP_SOURCES} )
    file(RELATIVE_PATH filename ${CMAKE_CURRENT_SOURCE_DIR} ${sourcefile})
    string( REPLACE ".cpp" "" file ${filename} )
    add_executable( ${file} ${sourcefile} )
    target_link_libraries( ${file} ${OpenCV_LIBS} )
endforeach( sourcefile ${APP_SOURCES} )